Process of removing tin from the surface of other metals.



s p usedis loosely held, and under the action of UNITED STATES PATENTEFIcE.

. ASAHELIK. EATON, OF NEW YORK, N. Y., nssrcrvon TO HUGH M. EATON,

OFBROOKLYN, NEW YORK.

PROCESS OF REMOVING TIN FROM THE SURFACE OF OTHER METALS.

SPECIFICATION forming part of Letters Patent N 0. 723,197, dated March17, 1903.

Application filed January 9, 1903. Serial No. 138,341. (No specimens.)

\ face of-other Metals,f which the following is a specification. 3

Myinvention relates to what is known in the art as detinning, and hasfor its object to remove metallic tin from the surface of other metals,particularly for the utilization of tinscrap by recovering the tintherefrom.

To these ends it consists of the method hereinafter described, and moreparticularly pointed out in the claims.

In trying on a practical scale a number of solvents I have found themost suitable and also the most economical to be sodium bisulfate, acompound commonly known in its crude state as salt cake or niter cake.This'salt is a residue from the manufacture of nitrate and hydrochloricacids and is always plentiful, and therefore comparatively tion.

low price.

In carrying out my process I prefer to follow the steps now to be setforth, though it is obvious, of course, that the same may be Variedconsiderably Without departing from the spirit of my invention-as, forexample, the proportion of solvent used in the b th must be determinedlargely according to t e character ofthe material on which the solventis to work. This, however, can be readily determined by any personskilled in the art who undertakes to practice my inven- I first dissolvefourteen hundred pounds of sodium bisulfate in seven hundred gallons ofwater, and into this put one ton of material to be worked, such asscraptin. I The whole is then subjected to a boiling temperature forabout four hours, after which the solution is transferred to another lreceptacle, as a crystallizing-tank, and then if it is found that someofthetin remains on the scrap a sufficient quantity of fresh soi lution isthrown thereonand heated until the last portions of the tin are removed.The reaction involved thus far is as follows: The extra equivalent ofsulfuric acid in the bi-salt heat its affinity for tin is sufficient tocause a complete combination with that metal, leaving a simple sodiumsulfate as a by-product.

Afterremoving the solution from the scrap metal the tin may be separatedout in metallic form at once; but 'I prefer to first concentrate thesolution to near the crystallizing point by further heating and thenallow it to t cool before further treatment. The liquid portion may thenbe drawn off from the crystals and used as a part of the solution withthe next lot of scrap, until the resulting solu tion of tin sulfate isof the desired strength, or the tin may be at once separated out inmetallic form by any of the Well-known processes, preferably byelectrolysis. A current of low tension, either from a battery or dynamo,readily deposits metallic tin upon the cathode in the form of sponge.

The by-product of the process, the simple sulfate of sodium, is inconstant demand, and therefore always marketable at a fair price. Indeedthis by-product is worth more commercially than the bisulfate firstused. The crystals of the simple sulfate which, as is well known, isGlaubers salt, from the original fourteen hundred pounds of bisulfateamount to about eighteen hundred pounds, the increased weight being dueto the added water of crystallization.

Thus far I have referred only to the use of bisulfate in an aqueoussolution. However, it may be used in many, if not most, cases,preferably in a state of fusion. The "chief advantage of the lattercondition is that the time of treatment is shortened from several hoursto .afew minutes. The chemical reactions are of course the same in bothcases.

It is evident, of course, that the equivalent potassium salt wouldaccomplish the same results in the process, but would not be so cheap.

The method specifically described above is compound of tin, andseparating out the tin in metallic form, as set forth.

2. The method of detinning tin-plate herein set forth, which consists inheating the tinplate in abath of sodium bisulfate to form a compound oftin, separating the bath and the metallic material from which the tinhas been dissolved, and then separating out the tin in metallic form, asset forth.

3.- The method of detinningtin-plate herein set forth, which consists inheating the tinplate in a bath of sodium bisulfate to form a compound oftin, separating and cooling the bath containing said compound, and thenseparating out the tin in metallic form, as set forth.

' 4. The method of detinning tin-plate herein set forth, which consistsin heating the tinplate in a bath of sodium bisulfate to form a compoundof tin, separating the bath containing said compound, and separating outtherefrom the metallic tin by electrolysis, as setforth.

ASAHEL K. EATON.

Witnesses:

, WM. H. CAPEL,

DRURY W. COOPER.

